FIG. 1 depicts a diagram of telecommunications system 100 in the prior art. Telecommunications system 100 comprises wireless telecommunications terminals 101 and 102; access points 103-1 through 103-M that serve basic service areas 110-1 through 110-M, respectively, wherein M is a positive integer; server 105; telecommunications terminal 106; and telecommunications network 100, interconnected as shown.
Telecommunications system 100 is capable of Session Initiation Protocol (or “SIP”) signaling. SIP is a standard protocol for initiating an interactive user session (i.e., a “call”) that involves multimedia elements such as voice, chat, video, and so forth.
Basic service area 110-m, for m=1 through M, is the service area in which shared access of other nodes in telecommunications system 100 is provided to telecommunications terminals such as terminals 101 and 102 As depicted in FIG. 1, basic service area 110-m is in an IEEE 802.11 wireless local area network. In area 110-m, the one or more wireless telecommunications terminals that make up the basic service set of area 110-m are able to access other nodes in system 100 via a shared-communications channel supported by access point 103-m.
Telecommunications network 100 is a telecommunications network such as the Internet, the Public Switched Telephone Network (PSTN), and so forth. Network 100 comprises or is connected to one or more transmission-related nodes such as gateways, routers, or switches that are used to direct packets from one or more sources to the correct destinations of those packets.
The service provided by the path that links a first node with a second node is characterized by its “quality of service,” which, for the purposes of this specification, is defined as a function of the bandwidth, error rate, and latency from one node to another. For example, a shared-communications channel that links a wireless terminal such as terminal 101 with an access point such as access point 103-1 is subject to a quality-of-service level.
For the purposes of this specification, the “bandwidth” from one node to another is defined as an indication of the amount of information per unit time that can be transported from the first node to the second. Typically, bandwidth is measured in bits or bytes per second. For the purposes of this specification, the “error rate” from one node to another is defined as an indication of the amount of information that is corrupted as it travels from the first node to the second. Typically, error rate is measured in bit errors per number of bits transmitted or in packets lost per number of packets transmitted. For the purposes of this specification, the “latency” from one node to another is defined as an indication of how much time is required to transport information from one node to another. Typically, latency is measured in seconds.
Each of telecommunications terminals 101 and 102, as well as terminal 106, is a communications device such as a local area network telephone, a notebook computer, a personal digital assistant [PDA], a tablet PC, and so forth. Each telecommunications terminal has an associated contact identifier (e.g., telephone number, email address, Internet Protocol address, etc.) that uniquely identifies that terminal in the address space of telecommunications system 100. Terminals 101 and 102 communicate, through one or more access points 103-1 through 103-M, with other telecommunications terminals that have connectivity with network 100, such as terminal 106. For example, terminal 101 is presently associated with access point 103-1 as depicted in FIG. 1 and uses the corresponding shared-communications channel to communicate wirelessly with other devices. In order to communicate, a user at a first telecommunications terminal in system 100, such as terminal 101, places a “call” (e.g., voice call, email, text chat, video, etc.) to a user at a second terminal in system 100, such as terminal 106. Terminals 101 and 102 are also capable of communicating with each other with call control signaling being routed through one or more nodes connected to network 100, as described below.
Each telecommunications terminal may use a “codec,” as is known in the art, to more efficiently transmit user information, such as voice signals, by compressing the transmitted information and decompressing the received information. A codec has an associated “codec rate” that specifies how much (compressed) information actually has to be transmitted per unit time.
Server 105 is a Session Initiation Protocol (SIP) proxy server that interacts with other nodes in setting up and managing calls. For example, server 105 is able to receive a call setup message (a SIP INVITE message) from terminal 101 as the result of terminal 101's user initiating a call attempt. The message is accompanied by (i) a traffic stream description (e.g., a SIP Real-Time Protocol [RTP] payload type, etc.) that specifies the nature of the call and (ii) the user identifier of the person being called.
System 100 has to be able to determine whether to admit each call. Call admission control is necessary, considering that terminal 101 is also competing with other terminals in its basic service area (i.e., area 101-1) for the shared-communications channel provided by access point 103-1. In fact, each of access points 103-1 through 103-M has to be able to handle multiple traffic streams—each stream comprising a series of packets—that are transmitted to or from wireless terminals via the corresponding shared-communications channel.
Furthermore, some of the terminals are capable of mobility. As a mobility-capable terminal moves closer to or away from an access point (e.g., access point 103-1, etc.), the maximum data rate at which the terminal is able to communicate with the access point changes during a call. When the terminal is close to the access point, the signal is generally stronger and, as a result, the maximum data rate is higher. Likewise, when the terminal is far from the access point, the signal is generally weaker and, as a result, the maximum data rate is lower. As a result, the actual shared-communications channel bandwidth that the terminal utilizes—that is, the channel occupancy used by the terminal-during a call changes over time. Furthermore, there can be multiple terminals using the shared-communications channel for calls, where each terminal is able to move independently of one another during a call.